The present invention relates generally to devices for spreading the human palate, and deals more particularly with a device which fits conveniently well up in the patient's palatal cavity, and which device allows for a relatively high expansion ratio within the anatomical confines of the patient's mouth such that one sized device can be used regardless of the particular individual's palate geometry and palatal expansion needed.
Devices for biasing the upper teeth of a patient, and thereby spreading the palatine bone segments in order to correct orthodontic deformities in the patient's dental structure are well known. Many such deformities can be corrected by spreading the palatine bone segments and allowing spontaneous repositioning of the teeth in conjunction with spreading of the bone segments, whereby to correct these deformities. However, those devices which are available for that purpose are either unduly cumbersonme, or may require removal and replacement in order to achieve the necessary desired palatine expansion.
For example, available orthopedic devices sometimes include a structure involving separate guide pins which not only complicate the assembly steps necessary for such appliances, but also serve to reduce the strength thereof. For instance, the function of such guide pins is to avoid rotary movement of main body sections of the appliance usually resulting from the reacting of adjustments made to these sections is achieving the expanding function. A common form of expansion device is the type having a spindle which is threaded at both ends, but in opposite directions, and which is oriented laterally in the patient's palatal cavity. This configuration of the spindle requires that it be spaced downwardly from the roof of the patient's mouth with the result that it is likely to interfere with normal movement of the tongue, an especially aggravating situation while eating or the like. In such a device, rotation of the spindle causes the two elements to move either toward or away from one another, and associated rods or wires are provided in association with these two elements in order to connect these separable elements with the patient's upper teeth. The two elements, at least initially during the tooth movement process, are spaced relatively close to one another, with the distance increasing as the teeth are separated in response to forces supplied by the appliance on the teeth. When the elements are spaced from each other a distance substantially corresponding to the length of the threaded spindle, the particular expansion device cannot serve any further purpose because of the fact that further expansion of the elements results in the disengagement of the threaded spindle from the elements themselves. Therefore, the patient is required to revisit the orthodontist, and new elements are required to be inserted, or a new spindle, all of which takes time and tends to raise the cost of the treatment process.
Thus, the disadvantages inherent in prior art expansion devices are directly associated with the difficulty and expense involved in interchanging components of these devices during the treatment period. These disadvantages are significant in the palatal expansion treatment process, because advantage must be taken of the biologic phenomenon that two to three weeks are required after a forced system is applied to a tooth for the remodeling mechanisms to occur that result in tooth movement.
The force applied by means of a palatal expansion device is initially dissipated by separation of the palatine bones at the mid-palatal suture if a large enough magnitude of force is applied. This magnitude has been measured to be as high as 35 pounds. If actively applied, or if residual forces remain after three weeks of expansion therapy, the teeth to which the device is attached will tend to move within their bony confines due to the bony remodeling mechanisms. Thus, it will be apparent that a device which need not be removed for replacement of certain of its components will result in an improved treatment process. The palatal expander device disclosed herein makes such an improvement possible.
The lateral width of the disclosed device in its initial (closed) position is much narrower than presently available devices for any given expansion ratio desired. Therefore, the present invention can be initially placed higher in any patient's palatal vault than presently available devices. This higher aspect results in a more favorable moment-to-force ratio (by the law of transmissability of forces) being applied to the teeth, and thereby, during the first three weeks of expansion therapy, to the palatine bones. The more favorable moment-to-force ratio results in more parallel expansion of the palatine bones in the patients' frontal plane. Further, the more favorable moment-to-force ratio is of considerable advantage during the inactive phase of palatal expansion therapy, after the first three weeks of active expansion, when the device is left in position in an inactive holding state for 90 days while allowing bony remodelling at the palatine suture to be completed. The poorer moment-to-force ratios in presently available devices, with the transmitted holding force passing occlusal to the center of resistance of the attached tooth roots, allows the expanded palatine bones to relapse somewhat as the biological bony remodelling mechanism acts about the tooth roots and the teeth move in a tipping manner through the bone as the bone collapses. In attempt to overcome the poorer moment-to-force ratio in order to have more parallel expansion of the palatine bone in the patient's frontal plane and to minimize the common relapse of bony expansion during the inactive holding phase, present devices are sometimes fabricated with molded acrylic contacting the palatal vault tissue. However, the contact of the acrylic with the tissue sometimes results in pressure necrosis of the palatal tissue when present devices are fabricated in this manner, a not surprising finding when it is realized that force levels of up to 35 pounds are involved. The more favorable moment-to-force ratio of the present invention eliminates these problems. The transmitted holding force passes through or apical to the center of resistance of the attached tooth roots. Therefore, any relapsing bony movement would involve pure translation or root movement of the attached teeth, slower and more difficult movements, resulting in less bony relapse of the expanded bony segments during the passive holding phase of therapy.
All presently available devices are activated by inserting a length of wire into the device's lead screw from the anterior end of the mouth and pushing the wire towards the throat to rotate the lead screw. This is an uncomfortable and psychologically stressful movement. The present device, due to its unique construction, is activated by inserting a length of wire into the device's lead screw in the anterior end of the mouth, but pushing the wire laterally right to left, a far more comfortable and less psychological stressful movement.
The unique construction of the present invention allows the user orthodontist to place the device in unilateral cleft palate patients such that unilateral bony expansion of the collapsed bony segment in those patients can be achieved to restore the segments to normal arch form. Presently available devices are incapable of such unilateral action.